In a background art, in various fields of industries, it is widely required to crush so as to pulverize solid materials of foods, chemicals, fertilizers, drugs, minerals, metal products, or the like. In these crushing processes by performing a crushing process until a particle shape and a grain size distribution of a powder are within a certain range, for example in the food industry or the drug industry fields, the dissolving rate of a hardly soluble substance may be accelerated or the body absorbing property or the content uniformity in mixing a drug may be promoted. Further, in the mineral industry or the chemical industry fields, the bonding force may be increased in a material formed from compressing during compression molding, or the surface smoothness of a coated product may be improved.
Generally, in the above-described conventional crushing processes, an airflow type or a mechanical type apparatus is utilized. In the former case, a large volume of high-pressure compressed air is injected into a crushing section (where due to the high speed airflow, typically in a sonic velocity range, materials are crushed through impact with one another or a material is crushed through impact with a portion of a peripheral wall surface or the like). According to an airflow type of crushing apparatus, the influence of heat generation is negligible and materials can be crushed into ultra fine particles. However, a large amount of highly compressed air needs to be stably supplied. As a result, the airflow type of crushing apparatus requires a large volume compressor having a high horsepower. Consequently, the initial cost or running cost is increased. The latter type of apparatus is further classified as a rotation impact type of crushing apparatus (e.g., a roll mill, a hammer mill, a pin mill, or the like) or a tumbler type of crushing apparatus (e.g., a ball mill, a vibration mill, or the like). The rotation impact type of crushing apparatus is widely used. According to the rotation impact type of crushing apparatus, a rotating disk, having a blade at an outer periphery thereof, is rotated at a high speed in the crushing section. The crushing process performed by striking the material inputted into the crushing section and impacting the material against a portion of the peripheral wall face or the like. This mechanical type of crushing apparatus can achieve a relatively constant crushing efficiency with a comparatively low running cost.
Further, as an example of a mechanical type crushing apparatus, the technology disclosed in JP-A-2000-042438 is known. According to the disclosure, a rotating grindstone having a grinding and crushing surface is provided at a classifying section located between the crushing section and a discharging section. The classifying gap of the section is narrowly set. Further, the outer peripheral surface of a blade and the peripheral wall face (i.e., liner) of the crushing section are provided with grinding and crushing surfaces in the form of a grindstone. Thereby, the crushing efficiency is improved by intensifying the application of a crushing force with respect to the solid materials.